1. Field of the Disclosure
The present disclosure relates to an image scanning device that scans and performs shading correction in a document. The present disclosure also relates to an image forming device having this image scanning device. The present disclosure also relates to a method for correcting a pixel value in the image scanning device.
2. Description of Related Art
An image scanning device emits light from a light source, and sends light reflected off a document to an image sensor to obtain image data. An image scanning device may also be provided in an image forming device such as a multifunction peripheral, a copying machine, a FAX device, or the like. An image scanning device may also be installed with an attachable image sensor unit called a contact image sensor (CIS). This CIS unit may be provided with a rod lens array, in which rod-shaped lenses are lined up in a primary scanning direction. In such a case, the rod lens array must have the same length as the scanning width (primary scanning direction width). However, obtaining a special product to match the scanning width (a specially-ordered rod lens array longer than a standard product) can lead to high costs. As such, the practice exists of connecting a number of cut standard rod lens arrays in general use to create a rod lens array of a desired length. For example, in order to enable scanning of a tabloid-size or A3-size sheet, a rod lens array with a short width for scanning letter-size or A4-size sheets is cut, and a plurality of cut rod lens arrays are connected to obtain a tabloid-size or A3-size width rod lens array.
For instance, a technique such as that described below is known in relation to connecting rod lens arrays. Specifically, an image sensor unit is known that has a sensor substrate upon which a plurality of photoelectric conversion elements are mounted, a light source for illuminating a document, an imaging element for forming an image on the sensor substrate from light reflected off the document, and a frame supporting all of the above; wherein, in the imaging element, a plurality of rod lens arrays cut at at least one end in a lengthwise direction are connected to each other at the cut ends to yield a pre-determined scanning width; the frame has a retainer for retaining the rod lens arrays; and the retainer has a broad bottom surface at which the cut parts and/or connecting parts of the rod lens arrays are positioned, and has a burr recess provided along both walls of the retainer that reaches a higher end than the broad bottom surface. This configuration attempts to eliminate the effects of burrs, without the need to monitor the direction of the rod lens arrays before and after connection or to perform deburring, by providing clearance for burrs generated on the cut surfaces during cutting.
By cutting and joining together rod lens arrays, a rod lens array of a desired length can be inexpensively obtained. In general, the rod lens arrays are connected using an adhesive. However, gaps can form due to variations in adhesion or deviations during cutting.
Thus, ambient light other than the light reflected off of the document may reach the image sensor through these gaps. When the light source is lit, ambient light may be mixed with the reflected light from the document at light receiving elements within the image sensor located at the joints between rod lens arrays. Because of this, within the image data obtained from the image sensor, those pixels positioned at the joint sections between rod lens arrays becomes brighter by the amount of ambient light. The problem arises that when portions that are brighter than they should be continue into the secondary scanning direction, they may be perceptible as white or gray streaks (streaking).
A UV-curing adhesive may be used as the adhesive in order to fit the rod lens arrays closely together and bond them together immediately while maintaining them in a proper state. It is preferable that the adhesive cure within a short amount of time after being irradiated with UV light. Thus, a transparent UV-curing adhesive, which easily allows UV light to penetrate, is preferable. However, a transparent adhesive allows ambient light to penetrate.
In order to prevent ambient light from reaching the image sensor, the use of a non-transparent UV-curing adhesive is also conceivable. However, non-transparent adhesives may not readily harden upon UV exposure. Also, because a CIS-type image sensor unit has a shallow depth of field, the rod lens arrays must be strictly positioned, and there is a fixed limit on the amount of adhesive used, which may make it difficult to apply enough adhesive to fill all the gaps.
In the known image sensor unit described above, the possibility of ambient light entering through gaps and creating streaks also remains. When, for example, one attempts to introduce a sealant in order to fill all the gaps while avoiding any contamination of the rod lenses, the sealant must be introduced with great delicacy and accuracy, which requires more work and can lead to cost-related problems.